• Journal of Korea Foundry Society
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• v.41 no.3
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• pp.235-240
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• 2021

We present the effect of the critical cooling rate during rapid solidification on the nucleation of precipitates in an Fe₇₅B₁₃P₅Nb₂Hf₁C₄ (at.%) alloy. The thermophysical properties of the rapidly solidified Fe₇₅B₁₃P₅Nb₂Hf₁C₄ liquids, which were obtained at various cooling rates with various sizes of gas-atomized powder during a high-pressure inert gas-atomization process, were evaluated. The cooling rate of the small-particle powder (≤20 ㎛) was 8.4×10⁵ K/s, which was 13.5 times faster than that of the large-particle powder (20 to 45 mm; 6.2×10⁴ K/s) under an atomized temperature. A thermodynamic calculation model used to predict the nucleation of the precipitates was confirmed by the microstructural observation of MC-type carbide in the Fe₇₅B₁₃P₅Nb₂Hf₁C₄ alloy. The primary carbide phase was only formed in the large-particle gas-atomized powder obtained during solidification at a slow cooling rate compared to that of the small-particle powder.

• Applied Chemistry for Engineering
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• v.28 no.4
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• pp.432-436
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• 2017

Carbon blocks were prepared by compression molding process using the mixture of isotropic cokes and binder pitches, which were reformed with different ${\beta}$-resin contents from pyrolysis fuel oil. Physical and chemical properties and also thermal behavior of binder pitches were investigated through elemental analysis, FT-IR and thermogravimetric analysis, respectively. The adhesion of binder pitches to isotropic coke particles was evaluated from SEM images of the fracture surface of carbon blocks. From these results, it is shown that the adhesion between the cokes and binder was enhanced by increasing the ${\beta}$-resin content of binder pitches. The density of the carbon block after carbonization also increased from 1.325 to $1.383g/cm^3$ by increasing the ${\beta}$-resin content of binder pitches from 1.4 to 20.1%.

• Journal of Energy Engineering
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• v.8 no.1
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• pp.189-201
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• 1999

범용 열가소성 플라스틱(polyethylene(PE), polypropylene(PP), polystyrene(PS), polyethylene-terephthalate(PET), acrylonitrile-butandiene-styrene(ABS))과 폐윤활유의 동시처리 열분해반응 실험을 수행하였다. 반응실험은 40$m\ell$ 용량의 회분식 미분반응기(microreactor)를 이용한 실험과 1리터 용량의 autoclave를 이용한 실험의 두 가지로 구분하여 행하였다. 전자의 경우는 통계적 실험적계획법(statistical experimental design)의 하나인 회전계획실험(rotatable design experiments)으로서 오각형 실험계획(pentagonal experimental design)에 의거한 반응변수 실험을 수행한 후 반응표면(response surface)을 회기분석법에 의하여 분석함으로써 최대의 오일 수율을 얻을 수 있는 최적 반응조건을 추적, 결정하였다. Autoclave 반응실험의 기본적인 목적은 실제 연속공정에 있어서 열분해 반응기 거동을 모사하기 위한 전초단계로서 충분한 시료의 확보를 통하여 이 때 생성된 연로유의 체계적인 분석(비등점분포특성, 진공증류, 기체분석, 원소분석, 발열량, 비중 등)을 행함으로써 연료유 수율 및 품질을 모사하고자 하였다. 미분반응기 실험에 있어서 주 범용열가소성수지인 PE, PP 그리고 PS는 각각의 최적반응조건하에서 거의 100%에 가깝게 오일로 전환되었지만 응축수지인 PET와 그래프트공중합수지인 ABS의 오일수율은 각기 78% 및 90%로서 상대적으로 낮게 나타났다. Autoclave를 이용한 실험의 경우 혼합플라스틱을 폐유에 대하여 40wt% 혼합하여 열분해하였을 때, 80wt% 오일, 15wt% 코우크, 그리고 나머지 5wt%는 탄화수소기체(C1-C6)로 전환되었다. 진공증류(252$^{\circ}C$,2 torr) 결과, 기/액-분리도는 3으로서 이는 생성오일의 75wt%가 경질연료유(가솔린, 등유, 경유)로 회수 가능하였다.

• Applied Chemistry for Engineering
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• v.31 no.3
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• pp.328-333
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• 2020

In this study, blended feedstock derived pyrolyzed fuel oil (PFO) and coal-tar was prepared to produce a pitch by thermal polymerization reaction for manufacturing artificial graphite materials. The aromaticity value of 0.355 and 0.818 was obtained for PFO and coal-tar, respectively. In addition, PFO and coal-tar exhibited the difference tendency of weight loss curve for thermogravimetric analysis, which is related to the structural stability depending on the aromaticity and functional groups. The production characteristics confirmed that the pitch derived PFO showed lower production yield and higher softening point than that using blended feedstock. In particular, when comparing P360 (138.5 ℃) and B420 (141.4 ℃) having similar softening points, the production yields of both pitches exhibited 29.89 and 49.03 wt%, respectively. This is mainly due to the blending of PFO and coal-tar having high pitch polymerization reactivity including a large amount of alkyl groups and coal-tar having high thermal stability. This phenomenon indicated that the increased production yield is because of a synergic effect of both the high reactivity of PFO and thermal stability of coal-tar.

• Fire Science and Engineering
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• v.25 no.3
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• pp.91-98
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• 2011

This study is about fire resistance performance of wood framed lightweight wall including a middle lintel as a traditional wall form in Korea. The target wall is non-loadbearing system which constructed with $38{\times}89$ mm ($2"{\times}4"$) wood frame and fireproof gypsum board covering, including a middle lintel made of $150{\times}150$ mm section glue-laminated timber. As a test results, all specimens have showed fire resistant performance over 90 minutes and tests were maintained until flame occuring on Specimen-l, 2, 3 at 91 min, 97 min and 98 min respectively. Fire resistance of the heat side gypsum board was 45 minutes and charring rate of middle lintel was equivalant with that of usual timber. The wood stud inside wall system showed relatively quick combution characteristic when exposed to high temperature with no temperature rising delaying time caused by moisture evaporation because of the dehydration preceded during the early period of fire side gypsum board resist to heat.

• Applied Chemistry for Engineering
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• v.10 no.6
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• pp.814-821
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• 1999

The specific capacitance characteristics of the electric double layer capacitors(ELDC) which were made of phenol based activated carbon fiber(ACF) electrodes. Also the effect of aqueous electrolytes on the cell performance has been investigated with respect to different specific surface areas of electrodes and different kinds of aqueous electrolytes. It has been shown that larger surface area and pore size, higher conductivity of electrodes, and higher ion mobility of electrolytes have better specific capacitances. It has been found that heat treatment at $1200^{\circ}C$ and $CO_2$ post-activation at $900^{\circ}C$ of the electrode are effective to improve the specific capacitance over 145F/g and 165F/g, respectively. The EDLC showed high efficiency and long cycle life over 30000 cycles.

• Journal of the Korean Vacuum Society
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• v.13 no.4
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• pp.157-163
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• 2004

Dependence of residual compressive stress of diamond-like carbon (DLC) films on relative humidity was investigated. Polymeric, graphitic and diamond-like carbon films were prepared by r.f.-PACVD using methane or benzene with the negative self bias voltage of the substrate ranging from -100 to -800 V. In-situ measurements of the residual stress were carried out in an environment chamber where the relative humidity was varied from 10％ to 90％. In dense DLC film of high residual compressive stress and hardness, we could not observe any change in the residual compressive stress with relative humidity. However, in the cases of graphitic and polymeric DLC films, abrupt change in the residual stress occurred by changing the relative humidity. The quantity of the stress change was inversely proportional to the film thickness, which means that the stress change with humidity is not due to the penetration of the water molecule into the film structure, but due to surface interaction between water molecules and film surface.

• Korean Journal of Materials Research
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• v.16 no.4
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• pp.241-247
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• 2006

Structural studies have been performed on precipitation hardening discovered in $L1_2-ordered\;Ni_3(Al,Cr)$ containing 0.2 to 3.0 mol% of carbon using transmission electron microscopy (TEM). Fine octahedral precipitates of $M_{23}C_6$ appeared in the matrix by aging at temperatures around 973 K after solution treatment at 1423 K. TEM examination revealed that the $M_{23}C_6$ phase and the matrix lattices have a cube-cube orientation relationship and keep partial atomic matching at the {111} interface. After prolonged aging or by aging at higher temperatures, the $M_{23}C_6$ precipitates then adopt a rod-like morphology elongated parallel to the <100> directions. Deformation at temperature below 973 K, typical Orowan loops were observed surrounding the $M_{23}C_6$ particles. At higher deformation temperatures, the Orowan loops disappeared and the morphology of dislocations at the particle-matrix interfaces suggested the existence of attractive interaction between dislocations and particles. The change of the interaction modes between dislocation and particles with increasing deformation temperature can be considered as a result of strain relaxation at the interface between matrix and particles.

• Applied Chemistry for Engineering
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• v.18 no.6
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• pp.580-586
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• 2007

In this study, 4 directional carbon/carbon composites with different preform architectures were manufactured and their thermophysical properties are studied. Carbon fiber preforms are fabricated with fiber bundles using four different spaces. The density of the fabricated preforms were increased through pressure impregnation and carbonizing process. The increased density of the composites was graphitized at $2300^{\circ}C$. Microstructures of these composite were observed under scanning electron microscope. This was to understand the effect the preform architectures has on the thermophysical properties of carbon/carbon composites. Also, the behavior of thermal conduction and heat expansion was investigated and studied in association with the factors of the reinforced direction of fibers and unit cell of preforms.

• Journal of Adhesion and Interface
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• v.14 no.2
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• pp.82-87
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• 2013

Preliminary studies on the synthesis of magnetic nanoparticles including nanoporous carbon materials have been done via a direct carbonization process from resol, ferric nitrate and triblock copolymer F127. The results show that the nanoporous magnetite/carbon ($Fe_3O_4$/carbon) with a low $Fe_3O_4$ content (1 wt%) possesses an ordered 2-D hexagonal (p6mm) structure, uniform nanopores (3.6 nm), high surface areas (up to 635 $m^2/g$) and pore volumes (up to 0.48 $cm^3/g$). Magnetite nanoparticles with a small particle size (10.2 nm) were confined in the matrix of amorphous carbon frameworks with superparamagnetic property (7.7 emu/g). The nanoporous magnetite/carbon showed maximum adsorption amount (995 mg/g) of ibuprofen after 24 h at room temperature. The nanoporous magnetite/carbon was separated from solution easily by using a magnet. The nanoporous magnetite/carbon material is a good adsorbent for hydrophobic organic drug molecules, i.e. ibuprofen.